Stabilized melt-processable ethylene/chlorotrifluoroethylene copolymer compositions

ABSTRACT

About equimolar ethylene/chlorotrifluoroethylene copolymer compositions are stabilized against thermal degradation so as to render them melt-processable by incorporating therein a fourcomponent stabilizing system comprising (a) a phosphite of an organic polyhydric phenol; (b) a salt of a carboxylic acid and a metal of Group II of the Periodic Table; (c) a thio dipropionic acid ester or alkali metal salt; and (d) an alkaline earth metal oxide.

United States Patent 1 Khattab STABILIZED MELT-PROCESSABLE ETI'lYLENE/CHLOROTRIFLUOROETHY- LENE COPOLYMER COMPOSITIONS [75] Inventor: Ghazi Khattab, Parsippany, NJ.

[73] Assignee: Allied Chemical Corporation, New

York, NY.

[22] Filed: Mar. 16, 1971 [21] Appl. No.: 124,911

[52] U.S. Cl.. 260/23 XA, 260/45.7 R, 260/45.75 R, 260/45.85 R, 260/45.95 D

[51] Int. Cl. C08f 45/62 [58] Field of Search 260/45.85, 45.95, 260/23 XA, 45.75, 45.7 R, 87.5

[56] References Cited UNITED STATES PATENTS 4/1966 Parker 260/23 10/1966 Hechenbleikner 260/23 1 Nov. 20, 1973 3,346,536 10/1967 Kauder et a1. 260/23 3,255,136 6/1966 Hecker et a1. 260/23 3,240,751 3/ 1966 Cannon et al. 260/45.7 3,501,446 3/1970 Ragazzini et 260/87.5 2,013,941 9/1935 Young et a1. 260/45.7

Primary ExaminerDonald E. Czaja Assistant Examiner-V. P. Hoke Attorney-Michael S. Jarosz [5 7 ABSTRACT 14 Claims, No Drawings STABILIZED MELT-PROCESSABLE ETIIYLENE/CHLOROTRIFLUOROETI'IYLENE COPOLYMER COMPOSITIONS BACKGROUND OF THE INVENTION This invention relates to stabilized, melt-processable ethylene/chlorotrifluoroethylene copolymer compositions, especially of about equimolar ethylene/chlorotrifluoroethylene copolymers, and more particularly, to a process for stabilizing about equimolar ethylene/chlorotrifluoroethylene copolymers against degradation during fabrication and use at elevated temperatures.

About equimolar ethylene/chlorotrifluoroethylene copolymers exhibit outstanding mechanical, electrical and chemical properties at high temperatures. For example, about equimolar ethylene/chlorotrifluoroethylene copolymers resist attack of most organic solvents at ambient as well as elevated temperatures, being only slightly soluble at l-l50C. in 2,5-dichlorobenzotrifluoride/benzonitrile or O-dichlorobenzene mixtures of :90 to 50:50 volume ratio. They are insoluble in bases and acids, including fuming nitric acid. These copolymers also possess high tensile strength and have melting points above about 220C. and as high as about 260C., which melting points are higher than those of the homopolymers of either ethylene (as high as 130C.) or chlorotrifluoroethylene (as high as 2l5C.). About equimolar ethylene/chlorotrifluoroethylene copolymers also have outstanding electrical properties.

tions, as extrusion or injection molding. About equimolar ethylene/chlorotrifluoroethylene homopolymers,

due to their high melting points in excess of about 220C., require melt fabrication temperatures of above about 250C., usually within the range of between about 260C. to 320C. At these high temperatures rapid degradation of the polymer occurs resulting in discoloration and loss of chemical, mechanical and electrical properties. In particular, degradation of these properties occurs during extrusion and injection molding operations.

Stabilizers which have been proposed to retard thermal degradation of trifluorochloroethylene polymers, such as zinc oxide, hydroquinone, chloranil, or mixtures thereof do not provide adequate stabilization of about equimolar ethylene/chlorotrifluoroethylene copolymers even when employed in amounts well above those in which such stabilizers are conventionally employed. Moreover, when zinc oxide is used in amount in excess of about 1 percent by weight of the polymer, the product is rendered white and opaque and has inferior mechanical and electrical properties. Use of hydroquinone and/or chloranil in amount above about 0.5 percent by weight of the polymer, either alone or in combination with zinc oxide, causes formation of bubbles in and intense discoloration of the polymer.

Stabilizers commonly used to retard thermal degradation of polyethylene, such as butylated hydroxy toluene, 1,1,3-tris-(2-methyl-4-hydroxy-5-tert.butylphenyl)butane or 4,4-n-butylidene-bis(6-tert.butyl-mcresol) do not provide protection against thermal degradation during melt processing of ethylene/chlorotrifluoroethylene copolymers having melting points in excess of about 220C.

It is an object of the present invention to provide a process for improving the thermal stability of ethylene- /chlorotrifluoroethylene copolymers.

Another object of. the invention is to provide meltprocessable compositions comprising ethylene/chlorotrifluoroethylene copolymers and stabilizers therefor.

More specifically, it is an object of the present invention to provide a process for improving the thermal stability of about equimolar ethylene/chlorotrifluoroethylene coplymers, and to provide melt-processable compositions comprising about equimolar ethylene/chlorotrifluoroethylene copolymers.

It is a further object of the present invention to provide melt-processable compositions comprising about equimolar ethylene/chlorotrifluoroethylene which are also resistant to thermal degradation on long term exposure to elevated temperatures.

Other objects and advantages will become apparent to those skilled in the art from the following description and disclosure.

DESCRIPTION OF THE INVENTION In accordance with the present invention, the thermal stability of ethylene/chlorotrifluoroethylene copolymers is improved by intimately dispersing within the polymer a four-component stabilizing mixture comprising (a) 0.01 to 30 percent by weight of the polymer of a transesterified reaction product of an organic polyhydric phenol having from 6 to about 50 carbon atoms and an organic phosphite triester free from phenolic hydroxyl groups having up to about 60 carbon atoms obtained by transesterification of the phenol and phosphite at an elevated temperature sufficient to form a homogeneous mixture; (b) 0.01 to 10 percent by weight of the polymer of a salt of a monocarboxylic acid having from about 6 to about 24 carbon atoms and a metal of Group II of the Periodic Table; (c) 0.0l to 10 percent by weight of the polymer of an ester or alkali metal salt of thiodipropionic acid; and (d) from 0.01 to 10 percent by weight of the polymer of an oxide of an alkaline earth metal, including magnesium.

Although each individual component, or the combination of any two components of the stabilizing mixture fails to effect satisfactory stabilization of ethylene/chlorotrifluoroethylene copolymers, and while a threecomponent mixture containing the above listed components, except the oxide of alkaline earth metal, effects excellentstabilization of the polymeragainst thermal degradation, not only during short-term exposure to elevated temperatures, as encountered during meltprocessing, but also in long-term exposure in use in high temperature environments, the four component stabilizing mixtures of the present invention which include an oxide of an alkaline earth metal, including magnesium, provide substantially better stabilization yet. The four component stabilizing systems of the present invention also do not adversely affect the physical and electrical properties of these copolymers.

Three component stabilizing systems for high melting about equimolar ethylene/chlorotrifluoroethylene copolymers comprising a phosphite of an organic polyhydric phenol, a salt of a carboxylic acid and a metal of Group 11 of the Periodic Table together with a thio dipropionic acid ester or alkali metal salt are described and claimed in commonly assigned copending US. Appl. Ser. No. 124,913 by Ghazi Khattab and Alfred Stoloff, Stabilized Melt-Processable Ethylene/Chlorotrifluoroethylene Copolymer Compositions," filed of even date herewith.

The ethylene/chlorotrifluoroethylene copolymers which may be stabilized in accordance with the present invention are high molecular weight, normally solid, thermoplastic polymers containing between 40 and about 60 mol percent of ethylene units in the molecule and having melting points between about 200 and about 265C. The stabilizing compositions in accordance with the present invention are particularly advantageous for use in about equimolar ethylene/chlorotrifluoroethylene copolymers containing between about 45 and about 55 mol percent of ethylene units and having melting points above about 220C.

These copolymers may be prepared by processes well known to those skilled in the art, as described, for example, in Hanford US. Pat. No. 2,392,378, which shows copolymerization of ethylene with chorotrifluoroethylene in a stirred aqueous medium at superatmospheric pressure using 'benzoyl peroxide as catalyst; in Nucleonics, September, 1964, pp. 72-74, disclosing formation of a high melting (237C.) 1:] alternant copolymer of ethylene and chlorotrifluoroethylene prepared using a radiation catalyst at C.; or British Pat. No. 949,422, showing bulk copolymerization of ethylene with chlorotrifluoroethylene at temperatures between 80 to +50C. using oxygen-activated alkyl boron catalysts; or Ragazzini et a1. U.S. Pat. Nos. 3,371,076 and 3,501,446, respectively relating to methods for making ethylene/chlorotrifluoroethylene copolymers using oxygen-activated boron-containing catalysts and to products obtained by that process. About equimolar ethylene/chlorotrifluoroethylene copolymers having high melting point above 200C. can also be prepared by batchwise bulk copolymerization of the monomers at temperatures of about 0C., say between about -20 to +20 C., at superatmospheric pressure in an agitator-equipped pressure vessel by charging the vessel with liquid chlorotrifluoroethylene monomer and bubbling gaseous ethylene into this monomer, using organic peroxide type initiators, such as trichloroacetyl peroxide and, if desired, adding small amounts of chain transfer agents, such as chloroform or heptane. The desired copolymer product is obtained as a dispersion in the monomer.

The organic polyhydric phenols used to obtain the transesterified reaction product used in the polymer compositions of the present invention have the formula:

wherein X is selected from the group consisting of oxygen, sulfur, alkylene, alicyclidene, arylidene and mixed alkylene-arylidene and alkylene-alicyclidene groups, wherein the aliphatic or cycloaliphatic portion of the molecule may be straight chain or branched chain, having from 1 to about 18 carbon atoms; wherein the R substituents, which may be the same or different, are independently selected from the group consisting of hydrogen and alkyl, straight or branched chain, having from 1 to about 18 carbon atoms; and wherein m and n are integers from 1 to 5, and 0 and p are integers from 0 to 4, with the proviso that the sums of m 0, and n p may not exceed 5. The OH groups preferably are in ortho and/or para position to X.

Transesterified reaction products of organic polyhydric phenols and organic phosphite triesters suitable for use in the presently claimed invention are described, for example, in US. Pat. Nos. 3,244,650 and 3,255,136, both issued to Hecker et al. The description of these transesterification products given herein is principally based on that given in Hecker et al.s U.S. Pat. No. 3,244,650.

As described in U.S. Pat. No. 3,244,650, suitable polyhydric phenols include orcinol, catechol, resorcinol, p-octyl resorcinol, p-dodecyl resorcinol, p-octadecyl catechol, p-isooctyl-phloroglucinol, pyrogallol, hexahydroxy benzene, p-isohexyl-catechol, 2,6-ditertiary butyl resorcinol, 2,6-diisopropyl phloroglucinol, methylenebis-(2,6-ditertiary butyl-m-cresol), methylenebis-(2,6-ditertiary butyl phenol), 2,2-bis(4- hydroxy phenyl) propane, methylenebis(p-cresol), 4,4- -benzylidene-bis(2-t-butyl-5-methylphenol), 2,2- methylenebis-(4-methyl-6-l -methylcyclohexylphenol), 4,4-cyclohexylidene-bis-(2-t-butylphenol), 2- ,6-bis( 2 -hydroxy-3 '-t-butyl-5 '-methylbenzyl-4- methylphenol, 4-octyl pyrogallol, and 3,5-ditertiary butyl catechol.

Especially preferred polyhydric phenols are 4,4'-nbutylidene-bis-(6-tert.-butyl-m-cresol) and 1,1 ,3- tris(2-methyl-4-hydroxy-5-tert.-butylphenyl)butane.

Organic phosphites suitable for making the transesterified reaction products or organic polyhydric phenol and organic phosphite triester used in the stabilizer compositions of the present invention are also described in US. Pat. No. 3,244,650. They can be any organic phosphite having the formula: (Ra) P wherein a is selected from the group consisting of oxygen, sulfur and mixtures thereof, and R is selected from the group consisting of aryl, alkyl, cycloalkyl, aryl-alkyl, alkylaryl and combinations thereof. The term organic phosphite triester, as used herein, includes oxo, thio and mixed oxo-thio phosphites. For reasons of availability, the phosphite will not usually have more than carbon atoms. Exemplary suitable phosphites include those listed in US. Pat. No. 3,244,650, i.e., monophenyl di-2-ethyl hexyl phosphite, diphenyl mono-2-ethyl hexyl phosphite, di-isooctyl monotolyl phosphite, tri-2-ethyl hexyl phosphite, phenyl dicyclohexyl phosphite, phenyldiethyl phosphite, triphenyl phosphite, tricresyl phosphite, tri(dimethylphenyl) phosphite, trioctadecyl phosphite, triisooctyl phosphite, tridedecyl phosphite, isooctyl diphenyl phosphite, diisooctyl phenyl phosphite, tri(t-octylphenyl) phosphite, tri(t-nonylphenyl) phosphite, benzyl methyl isopropyl phosphite, butyl dicresyl phosphite, isooctyl di(octylphenyl) phosphite, di(2-ethylhexyl) (isooctylphenyl) phosphite, tri(2-cyclohexylphenyl) phosphite, tri-alpha-naphthyl phosphite, tri(phenylphenyl) phosphite, tri(2-phenylethyl) phosphite, tridodecyl thiophosphite, tri-p-tert.-butyl phenyl thiophosphite, dodecyl thiodiphenyl phosphite and tert.-butyl phenyl thio-di-2-ethylhexyl phosphite.

The transesterified reaction products of organic polyhydric phenols and organic phosphite triesters free from phenolic hydroxy] groups may be obtained by heating together the phenol and phosphite ester, preferably at temperatures of from 100 to 200C., if necessary under reflux. To expedite transterification it is preferred to add a small amount of an alkali or alkaline earth metal oxide, hydroxide or phenolate, in amount of between about 0.05 to about 1 percent by weight. Although it is not necessary that transesterification be complete, it is believed that only the transesterification product is suitable for use in stabilizing about equimolar ethylene/chlorotrifluoroethylene copolymers during melt processing in accordance with the present invention because only they have sufficiently high boiling points to ensure their presence during fabrication by melt processing at temperatures of up to about 320C. Usually, transesterification involving about one-third of the phosphite ester groups of the triphosphite and about one-half of the available phenol groups of the dihydric phenol on a mol for mol basis, may be sufficient.

The second essential component of the stabilizer system of the present invention is a salt of a monocarboxylic acid having from about 6 to about 24 carbon atoms and a metal of Group II of the Periodic Table. The metal can, for example, be any one of zinc, calcium, cadmium, barium, magnesium, and strontium. The acid can be any organic monocarboxylic acid having from 6 to about 24 carbon atoms which does not contain nitrogen. Suitable acids are also described in US. Pat. No. 3,244,650. As therein set forth, the aliphatic, aromatic, alicyclic and oxygen-containing heterocyclic organic acids are operable as a class. Aliphatic acid includes any open chain carboxylic acid, unsubstituted or substituted with unreactive groups such as halogens, sulfur or hydroxyl. Alicyclic acid" includes any carbocyclic acid having a non-aromatic ring optionally substituted by an unreactive substituent, such as halogens, hydroxy] groups or alkyl and alkynyl radicals or other carbocyclic ring structures. Suitable aromatic acids can be carbocyclic or oxygen-containing heterocyclic and may be substituted by an unreactive ring substituent such as halogens, alkyl or alkenyl radicals and other saturated or aromatic rings condensed therewith. Suitable exemplary organic acids include those listed in US. Pat. No. 3,244,650, i.e., hexoic acid, 2- ethylhexoic acid, n-octoic acid, isooctoic acid, capric acid, undecyclic acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, oleic acid, ricinoleic acid, behenic acid, chlorocaproic acid, hydroxy capric acid, benzoic acid, phenylacetic acid, butyl benzoic acid, ethyl benzoic acid, propyl benzoic acid, hexyl benzoic acid, salicylic acid, naphthoic acid, 1- naphthalene acetic acid, orthobenzoyl benzoic acid, naphthenic acids derived from petroleum, abietic acid, dihydroabietic acid, hexanhydrobenzoic acid, and methyl furoic acid.

Organic zinc salts are preferred for use in the stabilizer compositions of the present invention, zinc-2- ethyl hexylate being a specific example of a preferred organic zinc salt.

The third essential component of the stabilizing system of the present invention, the ester or alkali metal salt of thiodipropionic acid, has the general formula:

wherein R and R which may be the same or different,

are independently selected from the group consisting of hydrogen, alkali metals, straight chain or branched chain alkyl radicals having from 1 to 36 carbon atoms, cycloalkyl radicals having from 3 to 36 carbon atoms, alkenyl radicals having from 6 to 36 carbon atoms, aryl radicals and alkaryl radicals, with the proviso that not more than one of R, and R may be hydrogen. The alkyl, cycloalkyl, alkenyl, aryl and alkaryl radicals may be unsubstituted or may, if desired, contain unreactive inert substituents such as halogens. Exemplary R groups include lithium, sodium, potassium, methyl, ethyl, propyl, iso-propyl, butyl, isobutyl, t-butyl, amyl, isoamyl, n-octyl, isooctyl, 2-ethyl hexyl, t-octyl, decyl, dodecyl, octadecyl, allyl, hexenyl, linoleyl, ricinoleyl, oleyl, phenyl, xylyl, tolyl, ethyl phenyl, naphthyl, cyclohexyl, benzyl, cyclopentyl, methyl cyclopentyl, ethylcyclohexyl, and naphthenyl groups.

Exemplary suitable alkali metal salts and esters of thiodipropionic acid include monoand disodium thiodipropionate, monoand dipotassium thiodipropionate, mixed sodium-potassium thiodipropionate, monolauryl thiodipropionate, dilauryl thiodipropionate, distearyl thiodipropionate, butyl stearyl thiodipropionate, 2-ethylhexyl lauryl thiodipropionate, di-2- ethylhexyl thiodipropionate, diisodecyl thiodipropionate, isodecyl phenyl thiodipropionate, benzyl lauryl thiodipropionate, benzyl phenyl thiodipropionate, the esters of fatty alcohols obtained from tallow, cotton seed oil or soya-bean oil and thiodipropionic acid. These esters as a class are known compounds. Many are commercially available. All can be prepared by methods known to those skilled in the art involving esterification of thiodipropionic acid with the corresponding alcohol.

Especially preferred for use in the composition of the present invention are disodium thiodipropionate, distearyl thiodipropionate, and dilauryl thiodipropionate.

The fourth essential component of the stabilizer system of the present invention is an oxide of an alkaline earth metal, including magnesium. It includes the oxides of calcium, strontium, barium and magnesium.

As above stated, the transesterified reaction product of an organic polyhydric phenol and the organic phosphite triester is employed in amounts within the range of about 0.01 to about 30 percent by weight of the polymer. It is preferably employed in amount ranging between about 0.05 to 6 percent by weight and more preferably yet, 0.1 to about 1 percent by weight.

Although the salt of the monocarboxylic acid and Group II metal may be employed in amount of 0.01 to 10 percent by weight of the polymer, it is preferred to employ 0.01 to 3 percent, and, more preferably yet, 0.02 to about 0.5 percent. In most preferred embodiments the weight ratio of the transesterified reaction product of the organic polyhydric phenol with the organic-phosphite triester and the Group II metal salt of the monocarboxylic acid ranges between about 4:1 to about 2:1.

The salt or ester of thiodipropionic acid is usually employed in amount ranging between about 0.01 to about 10 percent by weight of the polymer. It is preferably employed in amounts between about 0.05 and about 3 percent by weight, more preferably yet in amounts ranging between about 0.1 and about 1 percent by weight of the polymer.

The oxide of alkaline earth metal is added in amount ranging between about 0.01 and about 10 percent by weight, preferably between about 0.1 and about 1 percent by weight.

These stabilizers are admixed with the copolymer using conventional mechanical procedures. The order of addition of the individual components of the stabilizer system has no influence on its effectiveness. The individual components can be added separately or be mixed prior to addition with equally effective results. Stabilizer components can be added in solution or be dry blended with the copolymer. Liquid or soluble components of the stabilizer system can be admixed with polar organic solvents containing no hydroxyl groups, such as ketones and ethers, as well as with nonpolar aliphatic or aromatic solvents, such as hexane, heptane or toluene, and be sprayed onto the polymer if in finely divided form in conventional tumbling or blending devices. For molding operations, such as extrusion or injection molding, the blended mixture may be passed through an extruder and the extruded rod chopped into pellets of desired size. Alternatively, the stabilizers may be admixed with the copolymer by tumbling pellets of the copolymer, adding liquid components of the stabilizer system, tumbling again to distribute the liquid portions of the stabilizer, then adding the dry components of the stabilizer, continuing tumbling to distribute the dry components evenly over the surface of the pellets, and then extruding the resultant mixture to intimately blend the copolymer and stabilizers.

DESCRIPTION OF PREFERRED EMBODIMENTS Of the following experiments, those employing the four-component stabilizer system of the present invention illustrate specific preferred embodiments and illustrate the outstanding stabilization achieved by the stabilizing mixtures of the present invention.

The thermal stability of stabilized and unstabilized ethylene/chlorotrifluoroethylene copolymers was determined using the following procedures:

A. Infrared Method A one-mil film of the ethylene/chlorotrifluoroethylene copolymer is prepared by compression molding of copolymer powder in a Loomis Engineering Press or Carver Press at 260-270C. under loads of 8,000 to 15,000 lbs. The film is mounted on a suitable support and its infrared spectrum is recorded. The specimen is then thermally annealed in a forced draft oven in air at 200C. for specified periods of time and its infrared spectrum is again recorded. The development of carbonyl peaks in the 1,700 cm region is observed with time of annealing. Using absorbence at 3,000 cm as internal standard, ratio of peak absorbence at 1,700 cm to peak absorbence in the 3,000 cm region is an indication of degree of oxidation of the copolymer. It was found that multiple peaks appear at the frequency range of 1,650 to 1,800 cm during annealing in air at 200F. the magnitude of which increases with increasing annealing time.

To demonstrate its thermal instability, an equimolar ethylene/chlorotrifluoroethylene copolymer containing about 50 mol percent of ethylene units and correspondingly about 50 mol percent of chlorotrifluoroethylene units, having a melting point of 245C. and containing no stabilizers was subjected to thermal stability test using the above-described infrared method. Results are shown in Table I below:

TABLE I 1.R. LR. Annealing Time absorbence absorbence Absorbence in Air at 200C. 3,000 cm 1,700 cm" Ratio hrs. (a) (b) b/c O 0 0 20 0.132 0.013 0.1 27 0.190 0.035 0.184 0.189 0.088 0.465 114 0.184 0.177 0.636 138 0.184 0.153 0.832 168 0.180 0.187 1.04

A plot of annealing time vs. absorbence ratio shows a straight line indicating a fast rate of thermal oxidation of the copolymer almost immediately upon start of thermal annealing. Hence, it is clear that the unstabilized copolymer had no initial stability against thermal degradation.

When the unstabilized copolymer used in the above stability test is melt fabricated by extrusion at 270C., then the extrudate is discolored, contains voids, and has a rough appearance and, hence, is not suitable for practical use in any of the applications indicated, supra. B. Volumetric Method It has been found that thermal degradation of ethylene/chlorotrifluoroethylene copolymers involves release of acidic gases. To quantitatively determine release of acidic gases upon exposure of the copolymer to elevated temperatures in the presence and absence of air (in nitrogen) 10 gram portions of the copolymer are introduced into a 50 ml. flask equipped with thermometer, an inlet tube for air or nitrogen, and an outlet leading into a known volume of 0.1N sodium hydroxide. The flask is immersed in an oil bath maintained at 260C., and Carrier gas (air or nitrogen) is introduced at a slow rate into the flask. Ten m1. portions of the 0.1N sodium hydroxide are withdrawn by pipette at periodic intervals and are titrated with 0.1N hydrochloric acid using methyl orange as indicator. The decrease in strength of the sodium hydroxide solution, with appropriate correction for volume loss of sodium hydroxide solution, is related to quantity of acidic gases evolved.

A portion of the unstabilized about equimolar ethylene/clilorotrifluoroethylene copolymer used in the above infrared test was subjected to the volumetric thermal stability test in air as well as in nitrogen atmosphere. The results are summarized in Table 11 below.

TABLE 11 (a) Air Atmosphere 0.1N HCl HX,mmolcs A r,min. titer, ml. evolved. 0 l0 0 15 9.70 1.47 15 9.50 2.40 15 9.25 3.52 15 9.05 4.37 15 8.90 4.95 15 8.90 4.95 15 8.55 6.23 15 8.35 6.93

(b) Nitrogen Atmosphere 0.1N HCl HX,mmoles A r,min. titer,ml. evolved.

These data, again, indicate that thermal degradation of the copolymer starts immediately upon exposure to elevated temperatures. They also show clearly that, surprisingly, thermal decomposition of the copolymer proceeds at a much more rapid pace in nitrogen than it TABLE "I does in air.

Yarious stabilizers known to be effective for stabili- Test stab Amount of Effective Service zation of ethylene or chlorotrifluoroethylene homou stabilize, p i d hrs, 200cc, polymers are incorporated into an equimolar ethylenel- 4 4 Mo bis 32: P 24 chlorotrifluoroethylene copolymer containing about 50 butyl metaci'esoli 0.3 24 mol percent of units derived from ethylene having a 3 bis er t 0 3 melting point of 245C. The blends so obtained are submy g f jected to the infrared test above-described. Results'are Distearylthiodipropionate 0.1 27 summarized in Table Ill, below. In this table the effec- 1$= g$ o5 tive service period is the period of time during which h and the absorbence peak ratio in the 1,700 cm and 3,000 epmmi'zed W W 24 5 Butylated hydroxytoluene 0 3 cm regions remains 0, indicating the period of stabiland ity against thermal oxidation. The stabilized composi- 6 f i p p w 8-5 27 tions are prepared by dry blending insoluble stabilizer components with the polymer in finely divided form in Zinc oxide 0.05 110 a ball mill, adding soluble stabilizer components in suit- 7 g able solvents, mixing the solution with the polymer, and Zinc oxide 0.2 160 stripping the solvent. 8

Dry powdered ethylene/chlorotrifluoroethylene c0- rm. butylphenyl)butane 0.25

polymer of about 40 mesh particle size containing 25 and Zmc-2-ethylhexylate 0.05

about percent of ethylene units having a melting and point of 245C. and a melt index of about 2, deter- Distearyl th iodipropionat e 0.15 540 mined according to ASTM Dl238-65, is mixed in a 9 gf' fzfgmjf igf ball mill for periods of l to 2 hours with various ter. butylphenyl)butane 0.25

30 and amounts of stabilizers, includ ng stabilizer systems ac zincamhymcxylate (m5 cording to the present invention. Portions of the resin and blends are then charged into a melt rheometer, as de- Dimflryl l;:1P 015 (between about t a a scribed in ASTM Dl238-T, maintained at 275C. Calcium oxide 03 800 and I200 and placed under 12,176 grams load. Cuts of the ex- TABLE IV discoloration developed after 24 hrs. at 200C.

Weight of 1 min. cut 01 Amount of extrudate, taken after stabilizer indicated period [min.], percent by normalized to g./10 mins. Appearance 0! Test wt., based extrudate at longest No. Stabilizer on polymer 5 30 60 indicated time period [PllOSJhilc of 1,1,3-tris(2-metliyl-4-liydroxy-dtert-butylphenyl)-butaiie 0. 22

an 10... zine-g-ctliylliexylate 0.08 2.2 2.3 1.3 1.8 Clear with bubbles.

an iDistearyl tliiodipropiouatc 0. 1 PhOSJlllte oi 4,4-n-butylidene-bis-(fi-tort.-butyl-in-cres0l) 0. 22

an 11... Zincaz-etliylhexylete 0.08 1.0 1.0 2.0 1.0 2.0 Do.

an Distearyl thiodipropionate 0. 1 PhOSllllitO of 4,4-n-butylidene-bis-(6-toi-t.-butyl-mcresol) 0.22

an 12 Zine-2-ethylhexylate 0. 08 2.4 2.2 2 1 1.3 Bubbles with intensely and discolored spots. Magnesium oxide 0.01 PhOSIhite of 4,4-n-butylidene-bis-(G-tert.-butyl-m-cresol) 0. 22

an 13..-" Zinc-Hthylhexylate 0. 08 2.2 2.2 2.4 2.4 2.5 Slightly off-White,

and 'no bubbles, smooth Calcium oxide 0. 3 surface. Phosihite oi 1,1.3-tris(2-methyl 4-hydroxy-fi-tert.-butylphenyl) -butane 0. 22

an 14"... zinc z-ethylhexylate 0. 0g 1.6 1.7 1.8 1.8 1.8 Clear with bubbles.

an Disodium thiodipropionate 0.1 Phos bite of 4,4-n-butylidene bis-(fi-tert.-butyl-m-cl'esol) 22 an 15..." Zincg-ethylhexylate .08 2.3 2.4 1.9 D0.

an Disodium thiodipropionate .1 Phosihite of 1,1,3-tris(2-inetliyl-4-hydroxy-5-tert.butylphenyl)-butane .22

an Zinc-Z-ethylhexylate .08 16..." an 2.3 2.3 {3 3.3 2.4 Slightly oil-white,

Disodium thiodipropionate ,1 no bubbles, smooth and surface. Calcium oxide 3 PilOSJhltl) of 4,4-n-butylidene bis-(6-tert.-butyl-m-cresol 22 an Zinc-2-ethylhexylate 08 17... and 2.2 2.2 2.4 2.4 2.5 U0.

Distearyl tliiodipropionate .1

and Calcium oxide 3 18... Calcium oxide .3 2.4 2 5 2.4 2.5 Smooth, with bubb es- As can be seen from the above data, the fourcomponent stabilizing system of the present invention effectively stabilizes the about equimolar ethylene/chlorotrifluoroethylene copolymer for periods of 2 hours or more at temperatures of 275C., whereas none of the other stabilizers and stabilizer systems effectively stabilizes this copolymer for periods longer than about l hour.

I claim:

1. A copolymer composition having improved ther mal stability which comprises an admixture of an ethylene/chlorotrifluoroethylene copolymer containing about 40 to about 60 mol percent of ethylene units and about 40 to about 60 mol percent of chlorotrifluoroethylene units, and

a. 0.01 to 30 percent by weight of the polymer of a transesterified reaction product obtained from 1 ,l- ,3-tris(2-methyl-4-hydroxyl-5-tert.- butylphenyl)butane or an organic polyhydric phenol of the formula wherein X is selected from the group consisting of oxygen, sulfur, alkylene, alicyclidene, arylidene and mixed alkylene-arylidene and alkylene-alicylclidene groups, wherein the aliphatic or cycloaliphatic portion of the molecule may be straight chain or branched chain, having from l to about 18 carbon atoms; wherein the R substituents, which may be the same or different, are independently selected from the group consisting of hydrogen and alkyl, straight or branched chain, having from 1 to about 18 carbon atoms; and wherein m and n are integers from 1 to 5, and 0 and p are integers from 0 to 4, with the proviso that the sums of m 0, and n +p may not exceed 5, and an organic phosphite triester free from phenolic hydroxyl groups having up to about 60 carbon atoms obtained by transesterification of the phenol and phosphite at an elevated temperature sufficient to form a homogeneus mixture;

b. 0.01 to percent by weight of the polymer of a salt of a monocarboxylic acid having from 6 to about 24 carbon atoms and a metal of Group ll of the Periodic Table;

c. 0.01 to l0 percent by weight of the polymer of an ester or alkali metal salt of thiodipropionic acid, and

d. 0.01 to 10 percent by weight of the polymer of an oxide of an alkaline earth metal or magnesium.

2. The composition of claim 1 wherein the copolymer is an about equimolar ethylene/chlorotrifluoroethylene copolymer.

3. The composition of claim 1 wherein the transesterified reaction product is obtained from an organic phosphite having the formula (Ra) P wherein a is selected from the group consisting of oxygen, sulfur and mixtures thereof, and R is selected from the group consisting of aryl, alkyl, cycloalkyl, aryl-alkyl and alkylaryl.

4. The composition of claim 3 wherein the copolymer is an about equimolar ethylene/chlorotrifluoroethylene copolymer.

5. The composition of claim 1 wherein the salt of a monocarboxylic acid is a zinc salt.

6. The composition of claim 3 wherein the salt of a monocarboxylic acid is a zinc salt.

7. The composition of claim 6 wherein the copolymer is an about equimolar ethylene/chlorotrifluoroethylene 8. The composition of claim 7 wherein the transesterified reaction product is a phosphite of 4,4-n-butylidene-bis(6-tert.-butyl-m-cresol) or 1,] ,3-tris( 2- methyl-4-hydroxyl-5-tert.butylphenyl)butane.

9. The composition of claim 1 wherein the transesterified reaction product is a phosphite of 4,4-n-butylidene-bis-(6-tert.butyl-m-cresol) or I, l ,3-tris(2- methyl-4-hydroxy-5-tert.-butylphenyl)butane, wherein the salt of a monocarboxylic acid is zinc-2- ethylhexylate, and wherein the ester of thiodipropionic acid is distearyl thiodipropionate.

10. The composition of claim 9 wherein the copolymer is an about equimolar ethylene/chlorotrifluoroethylene copolymer.

11. The composition of claim 1 containing 0.05 to 6 percent by weight of the polymer ofa phosphite of4,4- n-butylidene-bis(6-tert.-butyl-m-cresol) or l,l ,3-tris(2- methyl-4 hydroxyl-5-tert.-butylphenyl)butane, 0.01 to 3 percent by weight of the polymer of zinc-2- ethylhexylate, and 0.05 to 3 percent by weight of the polymer of distearyl dithiodipropionate.

12. The composition of claim 11 wherein the copolymer is an about equimolar ethylene/chlorotrifluoroethylene copolymer.

13. A copolymer composition according to claim 1 containing 0.1 to 1 percent by weight of the polymer of phosphite of 4,4'-n-butylidene-bis-(6-tert.-butyl-mcresol), 0.02 to 0.5 percent by weight of the polymer of zinc-2-ethyl-hexylate, 0.1 to 1 percent by weight of the polymer of distearyl dithiodipropionate, and 0.1 to 1 percent by weight of the polymer of calcium oxide.

14. The composition of claim 13 wherein the copolymer is an about equimolar ethylene/chlorotrifluoroethylene copolymer. 

2. The composition of claim 1 wherein the copolymer is an about equimolar ethylene/chlorotrifluoroethylene copolymer.
 3. The composition of claim 1 wherein the transesterified reaction product is obtained from an organic phosphite having the formula (Ra)3P wherein a is selected from the group consisting of oxygen, sulfur and mixtures thereof, and R is selected from the group consisting of aryl, alkyl, cycloalkyl, aryl-alkyL and alkyl-aryl.
 4. The composition of claim 3 wherein the copolymer is an about equimolar ethylene/chlorotrifluoroethylene copolymer.
 5. The composition of claim 1 wherein the salt of a monocarboxylic acid is a zinc salt.
 6. The composition of claim 3 wherein the salt of a monocarboxylic acid is a zinc salt.
 7. The composition of claim 6 wherein the copolymer is an about equimolar ethylene/chlorotrifluoroethylene
 8. The composition of claim 7 wherein the transesterified reaction product is a phosphite of 4,4''-n-butyl-idene-bis(6-tert.-butyl-m-cresol) or 1,1,3-tris(2-methyl-4-hydroxyl-5-tert.butylphenyl)butane.
 9. The composition of claim 1 wherein the transesterified reaction product is a phosphite of 4,4''-n-butyl-idene-bis-(6-tert.butyl-m-cresol) or 1,1,3-tris(2-methyl-4-hydroxy-5-tert.-butylphenyl)butane, wherein the salt of a monocarboxylic acid is zinc-2-ethylhexylate, and wherein the ester of thiodipropionic acid is distearyl thiodipropionate.
 10. The composition of claim 9 wherein the copolymer is an about equimolar ethylene/chlorotrifluoroethylene copolymer.
 11. The composition of claim 1 containing 0.05 to 6 percent by weight of the polymer of a phosphite of 4,4''-n-butylidene-bis(6-tert.-butyl-m-cresol) or 1,1,3-tris(2-methyl-4-hydroxyl-5-tert.-butylphenyl)butane, 0.01 to 3 percent by weight of the polymer of zinc-2-ethylhexylate, and 0.05 to 3 percent by weight of the polymer of distearyl dithiodipropionate.
 12. The composition of claim 11 wherein the copolymer is an about equimolar ethylene/chlorotrifluoroethylene copolymer.
 13. A copolymer composition according to claim 1 containing 0.1 to 1 percent by weight of the polymer of phosphite of 4,4''-n-butylidene-bis-(6-tert.-butyl-m-cresol), 0.02 to 0.5 percent by weight of the polymer of zinc-2-ethyl-hexylate, 0.1 to 1 percent by weight of the polymer of distearyl dithiodipropionate, and 0.1 to 1 percent by weight of the polymer of calcium oxide.
 14. The composition of claim 13 wherein the copolymer is an about equimolar ethylene/chlorotrifluoroethylene copolymer. 